Motor control system



May 7, 1935. N, H. WILLBY MOTOR CONTROL SYSTEM Filed June 21, 1955 INVENTOR Norman H. Willby.

WITNESSES:

Patented May 7, 1935 nonhuman-n21, 193: Serial iwsmus My inventioni'reiatesfiaeml'aliw, to motorcon- .trol systems, and, "moremartieulariy, .to systems .tor contrillling-fl'm acceierationoi theiwopelliag motors oneleetric Vehicles. I

The copending application-ct 3.0. Austin, N. .H. Willby and R. R. Serial No; 4013956, filednctobenfliiplmoand inglmuse *Electric -81 :Manufaotming Company describes! and claims at :eystem for automatically :ers modifications andimprvor the sysdisclosed in the Jorming appli- An object- 01' my invention, stated. is to :provide 1a .eontrol rsimpletand effloient imoperationand-whiehmey .be economically manutectured i andrinstalied.

A more specific objectoLmyJnvention-is to provide In the smooth operation of -an electric vehicle in-order that ahigh degree otoomfort {gnthe passeng ersonthe vehicle may-be -main- Another object of myiinvention is to provide acceleration of the vehicl the master controlleriis'in any-position.

Other objects of the invention will be described -fully hereinafter or will be apparent "to those 'Skiiiedinthe art.

and -the some application of which will be indicated in the cm For a fuller understanding or the nature anti objects of the invention, reference may be hail to the following detailed -Il8lcripflon, men in conjunction with the accompanying liming, in which:

figure 21 is a atic view showing the apparatus and the cimuits of s motor control system am my mention-and v I Fig. 215 a chart the sequence! operation out part of the apparatus ehomnxind'ig. 1. Relax-ring to the drawing, the system chasm comprises motors M and H, whichmiw be ore. type suitable for propelling electric vehicles. The motors illustrated are of the series he xeniesneld I! and I A system whichslhallibe lmeiswitch I4 is aprovidetl for connecting/the motors tone power conductor ii, *which'is'connectadwo a trolleyconductor"I6 by means of a 'i'roliey'll. I'he'troileycohduetor l6 maybe enrmized 1mm any: suitable "source of power, such aixeneratin'g station (not'shown) In 'aocorflance with :a, well --known practice, the motom f0 and H areconnecized inseriescircuit reiation to startthe vehicle. 'when it has Pbeen accelerated 'toa predetermined speed, -10 "the motors are connected in1mralle1 circuit V relation in order that "-the 'speed ofthe'c'ar may 'be hmreased further. =Electrieaiiy operated switches Ii, ilmnd 21 :areinmvided for estabikhing the necessary circuits to connect the 16 motom l0 und 'fl 1n eitlier *series "or parallel circult 1613121011.

A mummy: wesistormeotions ll, 22, "is and -24 rate provilied to control the acceleration of the motors l0 and II. "Accelerating switches 08,45, "26, 28mm 19 aredisposed to shunt the resistor iseetioms to melerate the motors in a hidnner' wellrknown inthemrt. I

In "order that th'e =acceleration 01' the motors may be automatioaliycontrolled, nmaui'i'ezit-lirriit "item! 3| which is respomive to the motor *cur- Xmnt, la unheated in the motor circuit. With a view to varying the rate 'of acceleration of the motors when =tramc 'conditions change and to'olttaitiing a higlior rate =01 acceleration when 30 Whig conditiom permit, the limit relay 3! la with 'a *s'erie's or actuating coil 32 and a 111111111103 of ldadingcoiis 83,14 and which arefl tooppose the actuating coil -82. 'Wheh 18408413180011813fl8 and 85 are 35 mews/me amount-of current required in the eoil -12 to Open the relay is increased thereby the ammmt of current permittedto 'the motors Ill and H 'during'each m or: acceleration and, consequently, 'inoreas- 40 1118 the rate of acceleration "bf the motors, as will "be described more fully hereinafter.

Tim-limit "relay fll cooperates with a sequence -8Wch M 'to'automatically -control the operabiom at the transfer and accelerating switches M to 48, inclusive. Bh'e sequence switch is austep-hy-step to control the weration -01 the :l oregoing switches upon the actuation -of ,a master controller *3! to set it in operation.- As illustrated, the sequence switch s a iplurality of contact fingers disposed to engage contact segments mounted upon a mum-which is actuated by their engine 38.

The operation of the air engine 38 is con- !h'olled by maonet valves 4-! and 12 which are actuated by coils 43 and 44, respectively. The air engine 38 is so constructed that the drum of the sequence switch 36 is advanced when both of the magnet coils 43 and 44 are energized. When both of the coils 43 and 44 are deenergized, the drum of the sequence switch is actuated toward position The drum of the sequence switch may be stopped and retained in any intermediate position by energizing the coil 43 and deenergizing the coil 44.

In order that the acceleration of the motors may be stopped at any time and the vehicle allowed to proceed at the speed previously attained, the master controller 31 is provided with a lost motion device which permits the operator to stop the sequence switch 36 at any time by a slight backward movement of the controller handle when the controller is in any position.

In previously known control systems, it has been necessary for the controller handle to be returned to a certainposition to stop the sequence switch and it'has been found that the operators frequently have difllculty in properly manipulating the controller to accomplish the desired results. By means of the present device, the operator may readily stop the acceleration of the vehicle at any time. A slightbackward movement of the controller handle interrupts the circuit through the magnet coil 44 and stops the sequence switch, as will be explained more fully hereinafter.

The mechanical construction of the lost motion device provided on the controller is fully described in Patent No. 1,700,602, issued January 29, 1929 to L. J. Stephenson and assigned to the Westinghouse Electric & Manufacturing Company. It is, therefore, believed to be unnecessary to describe the details of its construc tion in this application.

The master controller 31, which may be of the drum type having a plurality of contact fingers disposed to engage contact segments, also controls the energization of the line switch l4 which connects the motors to the power conductor l5. When the controller is actuated to the off position, the motors are disconnected from the power source.

In order that smooth operation of the car may be obtained and a high degree of comfort afforded the passengers when power is shut off from the motors while the car is accelerating rapidly, provision is made for inserting resistance in the motor circuit before the motors are disconnected from the power source. The resistance is inserted after the master controller has been returned to'the of! position to disconnect the motors. In this manner, the motor speed is gradually reduced thereby preventing the uncomfortable jolt experienced by the passengers when power is shut off during a high rate of acceleration. In the embodiment of the invention illustrated, two resistor sections 45 and 46 are provided for this purpose, however, additional resistors may be provided if desired. Electrically-operated switches 41 and 48 are provided for shunting the resistors 45 and 46. f

The energization of the actuating coils of th switches 41 and 48 is controlled by the master controller 31, but the switches are so interlocked with each other and with the line switch I4 that the line switch is closed first and then switches 41 and 48 in sequential relation. When the controller 31 is actuated to the off position, switch 48 is first opened and then switches conductors 92 and 83,

41 and H in sequential relation, thereby inserting the resistors 46 and 45 in the motor circuit before the motors are disconnected from the power source.

Assuming that it is desired to connect the motors l0 and H to the power conductor |5 to start the vehicle, the controller 31 is actuated to position I to establish an energizing circuit for the actuating coil of the line switch I4.

This circuit may be traced .from a conductor 5|,

which is connected to the power conductor |5, through contact fingers 52 and 53, bridged by a contact segment 54 on the controller 31, conductor 55 and the actuating coil of the switch M to a grounded conductor 56. At the same time a circuit is established for the actuating coil of the switch l8. This circuit extends from a contact finger 51, which engages the contact segment 54 on the controller 31, through conductors 58 and 58, an interlock 6| on the switch 20, conductor 62, an interlock 63 on the switch l9 and the actuating coil of the switch l8 to the grounded conductor 56. The closing of the switches l4 and I8 connects the motors l0 and II to the power source in series-circuit relation. The motor circuit may be traced from the power conductor I5 through contact members 64 on the switch l4, the resistors 45 and 46, conductor 65, the armature of the motor I0, the field winding l2, conductor 66, the resistors 2| and 22, conductor 61, contact members 68 on the switch |8, conductors 68 and 1|, the resistor 24, the conductor 12, the armature of the motor I the field winding I3, the actuating coil 32 of the limit relay 3| and conductor 14 to the grounded conductor 56.

' It will be seen that the motors I0 and H are connected in series-circuit relation and that the resistors 45, 46, 24, 2| and 22 are connected in series with the motors thereby causing them to rotate at a relatively slow speed. The motors may be accelerated by actuating the controller 31 to position 2 thereby establishing a circuit for the actuating coil of the switch 41. This circuit may be traced from a contact finger 15, which engages the contact segment 54 of the controller 31, through conductors 16 and 11, an,

interlock I8 on the switch I4 and the coil of the switch 41 to 56. The closing of on the switch 41 shunts the resistor 45 from the motor circuit.

When the switch 41 is closed, an energizing circuit is established for the actuating coil of the switch 48, which extends from a contact finger 8|, which engages the contact segment 54, through conductor 82, contact fingers 83 and 84. bridged by the contact segment 85 on the sequence switch 36, conductor 86, an interlock 81 on the switch 41 and the actuating coil of the switch 48 to the grounded conductor 56. The resistor 46 is shunted by contact members 88 when the switch 48 is closed.

It will be seen that the air engine 36 is energized to operate the sequence switch 36 when the controller 31 is actuated to position 2. As previously explained, the air engine 38 will advance the sequence switch 36 when both of the magnet coils 43 and 44 are energized. The magnet coil 43 was energized when the controller 31 was actuated to position I. The energizing circuit may be traced from a contact finger 8|, which engages the contact segment 54, through the actuating coil 43 of actuating the grounded conductor the contact members 19 F the magnet valve ill .and conductor 34 to the grounded conductor 88.

When the controller 31 is actmtedito position 2", the coil 44 of :the magnet valve fl isienergized through a circuit which :may be traced from the contact :nnger ill, through :conductor 82, contact "fingers and 86, :britkedby the contact segmentili, conductors 98 and 81,:con- :tact 'fingers "98 and 98, bridged by the contact segments, till 402 and ilm-which comprise the "lost motion" device previously described, eonductor I04, contact members 108 on the limit irelay :O'I, conductor M6, ithe actuating -coil 44 of 'the magnet valve- 42 and :conductor 94 do the grounded conductor 88.

The sequence switch 26 is advanoed'step-ibystep to operate the resistor shunting switches 26, 29 and i0, as indicated 'in'the sequence chart shown inl ign2. I

When the sequence switch is advanced -'to :position 4", :the actuating coil fthe switch '16 is energized throughia circuit which-extends rfrom the energized conductor GI through contact fingers I01 and IM, bridged iby a contact segment W9, conductor l and the-coil of the switch 25 to the grounded conductor '36. The resistor section "2| is shunted by the contact members %I i2 on the switch 25 when the switch isiclosed.

When-the sequence switch 26 is advanced to position ffl, an energizingcircuitIla-established for the actuating coil of the switch 29, which may be traced from a contact finger I I8,qwhich engages the contact segment t through conductor il I4 andthe coil-of the switch 29 to the :grounded conductor-:86. It will'be seen that the closing of the contact members MI 01' the 'switch .29 connects the resistors 24 and 24 in .parallel circuit relation, thereby permittingan :increase in the motor current and causing "the motors to accelerate.

The advancement of the sequence switch to iposition 56 energizes the actuating coll oi'the switch 26 through a circuit whichmay 'betraeed from a contact finger IIB, through conductor Illandthe coil of the switch-28 to the grounded conductor 56. The :resistor 22 is shunted by ;the closing of the contact members I-IO :or the switch 26.

When the. sequence switch '38 1 advances to position 1'7, the switch 19 isclosed *toshunt the resistors 23 and 24 from the motor circuit, thereby accelerating the motors to the maximum speed which can be attained with the motors connected in series-circuit relation. The energizing :circuit through the 0011 0! the switch i9 may be traced from a contact finger :9, through conductor MN :and the actuating coil of the switch 1I9 to :the .groundcdconductor 56.

As previously explained, the operation of the sequence switch 36 during the accelerating period is controlled by the limit relay 3|. It will be readily understood that the current in the motor circuit increases when resistance is shunted from :the motor ,circuit by "the closing of the acceleratingswitclres in the manner dust described. When the motor current increases above a predetermined value, the limit relay '3I is opened or raised to its uppermost positicn by the force exerted by .the :actuating coil '32, which is connected in the motortcircuit. The opening of the contact members I05, carried by the relay, interrupts 'the energizing :cirouit throughthe magnet coil -44 .of the .air xengine as, thereby stopping the advancement of the sequenceswitchxifi, as previously explained As the motors accelerate in speed their counterelectromotive force increases and the motor current is reduced, thereby permitting the :limit relay sl to drop to its lowermostposition, which permits lthesequence switch 36 to be advanced another step. :In this manner, the sequence switch ispermitted to advance step-by-stepunder the control of the limit relay 3I to accelerate the motors. I If it isdesired to further increase thespeed of the-.=motors I0 and II by connecting them inparallel circuit relation, the control1er-31 may be actuated to position 3,in which a contact finger I22 engages the contact segment :54, thereby keeping the conductors! energized and maintaining the circuit previously traced through the coil 44 of the magnet valve 42. The sequence switch 36, therefore, advances throughthe transition step to position 8, at :which time the switch 19 is opened and the switches 21 and 20 are closed to connect the motors and I I to the power source in parallelcircuit relation. The energizing circuit for the actuating coil of the switch 21 maybe traced from a contact finger I23 which engages the contact segment I09, through conductor I24, the coil of the switch 21, conductors I25 and 126 and an interlock I21 on the switch I8 to the grounded conductor 56; The circuit through the actuating coil of the switch 20 extends 'from acontact finger I28, through conductor I-29,the coil of the switch 20, conductors I25 and I26 and the interlock I21 to the grounded conductor 56.

The motors I0 and II are now connected in parallel-circuit relation, the circuit through the motor extending from the power conductor I5, through the contact members 64 of the switch I4, the contact members 88 of the switch 48, conductor 65, the armature winding of the 'mctor III, the field winding I2, conductor 86, the resistors 2| and 22, eonductor"61, the contact members I3'I on the switch 20 and conductor 14 to the grounded conductor 56. "The circuitthrough the motor 'II may be traced from the conductor '65 through the contact members -I32-onthe switch 21, the resistors 23 and 24, conductor 12, the armature of the motor II, the field winding I3, the coil "32 of :the limit relay 3| and conductor 14 to the 'grounded conductor '56. g

The motors I0 and II maybe permitted to accelerate ata normal rate by permitting the sequence switch '36 to advancethrough posiinclusive, to operate the accelerating'switches 25, 26, 28 and 29 to shunt -the resistors. 2|, 22, 23 and 24 in themanner previously described. The circuit through the actuating coil of the switch 28 may 'be traced from a contact finger I48, which engages the contact segment I019 on position I0 of the sequence switch 36ythr0ugh conductor I49 and thecoil 'of theswitch 28 to the grounded conductorSG. The circuits'through theactuating coils of the switches 25, 26 and29 havejbeen previously traced.

In order that a higher rate of acceleration may beobtained when traffic conditions permit, the limit-relay3 Lwhich, as previously'explained, controls the operation of the sequence switch -36 and thereby controls the rate of accelerationof the meters, is provided with the loading cells '33, "34 and 36, whichare disposed to oppose the actuating coil 32. The loading coil 33 is energized through a circuit which extends Erom the previously energized conductor 92, through contact fingers I33 and I34, bridged by contact segment I35, conductor I36, the coil 33 and a resistor I31 to the grounded conductor 56.

It will be observed that the controller 31 is provided with a contact segment I38, which is disposed to bridge contact fingers I4I, I42, I43 and I44 to energize the loading coils 34 and 35. When the controller 31 is actuated to position 4, the loading coil 34 is energized through a circuit which extends from conductor I36, through the coil 34, conductor I45, contact fingers I42 and MI, bridged by the contact segment I38, conductor I46 and resistor I31 to the grounded conductor 56.

When the controller 31 is actuated to position 5, the loading coil 35 is energized through a circuit which may be traced from the conductor I36, through the coil 35, conductor I41, contact fingers I43 and HI, bridged by the contact segment I38, conductor I46 and the resistor I31 to the conductor 5'6. The three coils 33, 34 and 35 are thereby energized to oppose the actuating coil 32 and increase the amount of current required to operate the relay 3i, which causes the motors I0 and II to be accelerated at a higher rate.

The rate of acceleration may be still further increased by actuating the controller 31 to position 6 to shunt the resistor I31 from the circuit through the loading coils 33, 34 and 35. When the controller 31 is on position 6, the contact finger I44 engages the contact segment I38 thereby connecting the coils 33, 34 and 35 directly to the grounded conductor 56, which increases the current flowing through the loading coils of the relay 3|, thereby permitting a higher amount of current to flow through the motors I0 and II.

In this manner, the operator of the vehicle can vary the rate of acceleration of the motors in accordance with trafiic conditions. The highest rate of acceleration is obtained by actuating the controller 31 to position 6 and lower rates of acceleration may be obtained by retaining the drum 31 on one of the intermediate positions.

With a view to preventing the sequence switch 36 from stopping between positions when the circuit through the contact members I05 is in terrupted by the operation of the limit relay 3|, a plurality of contact segments I5I are disposed to be engaged by a contact finger I52, while the sequence switch is being actuated from one position to the next, thereby maintaining the energizing circuit through the coil 44 of the magnet valve 42. In this manner, it is insured that the sequence drum 36 will not stop between operating positions.

In order that the operator may stop the sequence switch 36 on any position to prevent the further acceleration of the car, the masterv controller 31 is provided with the lost motion device previously mentioned. It will be observed that the contact segment I03, which is actuated by the handle of the controller 31, is disposed to engage the contact segments WI and I02 while the controller handle is being operated in a forward direction, thereby establishing the energizing circuit for the coil 44 of the magnet valve 42. By moving the handle of the controller a slight amount in the backward direction, the contact segment I03 will be disengaged from the contact segments IOI and I02 thereby interrupting the circuit through the coil 44 and stopping the sequence switch, as previously explained.

It will thus be seen that the operator can stop and hold the sequence switch on any position by a slight backward movement of the controller handle. This may be done irrespective of the position of the master controller and it is not necessary for the controller to be returned to a certain predetermined position, as has been required in previously known control systems, in order to stop the sequence switch.

When it is desired to resume the acceleration of the vehicle, it is only necessary for the operator to move the handle of the controller a slight amount in the forward direction to reestablish the energizing circuit for the coil 44 of the magnet valve 42, thereby permitting the sequence switch 36 to advance in the normal manner.

As is the usual practice, the motors may be disconnected from the power source to stop the car by returning the master controller 31 to the off position. However, in order to prevent the uncomfortable jolt which the passenger receives as a result of the sudden deceleration of the car when the power is suddenly shut off. the motors while the car is traveling at a rapid rate, the resistors 45 and 46 are inserted in the motor circuit before the line switch I4 is permitted to open to completely disconnect the motors from the power source.

When the controller is actuated to the oiI position, the energizing circuit through the actuating coil of the switch 48 is interrupted, which permits this switch to open, thereby inserting the resistor 46 in the motor circuit. However, the switches 41 and I4 do not open when the controller 31 is returned to the off position. The switch I4 is retained in the closed position by a holding circuit which extends from a contact finger I53, which engages the contact segment I08 of the sequence switch 36, through conductor I54, an interlock I55 on the switch 41, conductor 55 and the coil of the switch I4 to the ground conductor 56. The holding circuit for the actuating coil of the switch 41 may be traced from conductor 55, which is energized through the circuit just traced, through con ductor 156, an interlock I51 on the switch 48, conductor 11, the interlock 18 on the switch I4 and the coil of the switch 41 to the grounded conductor 56.

When the switch 48 opens, the holding circuit for the coil of the switch 41 is interrupted and this switch is then permitted to open, thereby inserting the resistor 45 in the motor circuit. Likewise, when the switch 41 opens, the holding circuit through the coil of the switch I4 is interrupted by the opening of the interlock I55 on the switch 41 and the switch I4 is then permitted to open to disconnect the motors from the power circuit. In this manner, the resistors 45 and 46 are inserted in the motor circuit for a short time in order to prevent the sudden decrease in the motor speed, thereby preventing the uncomfortable jolt experienced by the passengers on the vehicle when the power is suddenly shut off the motors.

In order to simplify the drawing and description of the control system, only two steps of resistance have been illustrated in connection with this feature, however, it will be understood that additional steps may be readily provided if desired. The switches which are provided for answers may be utilized for controlling: the operation of.

electric motors of various types" and which. is especially suitable for controlling the propelling; motors of electric vehicles. It is apparent that, the system hereindisclosedwill permit smoother operation of the vehicle thanpreviously known systems, thereby increasing thezcomtort of: the passengers on the vehicle;

I do not desirerto be. restrictedto the specific embodiment or arrangement on parts herein shown and described; since it isv evident that they-may be changed'and'modined without de-. parting from the spirit and; scope of my invention,.as definedin theappemied'.

I claim as my invention:

1. In a motor-control; system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a plurality of resistor sections connected in series-circuit relation and in series with the motor to control the motor current, switches for shunting the resistor sections, means for automatically accelerating the motor, a controller for controlling the energization of said switching means and said resistor-shunting switches independently of the automatic accelerating means, and electrical interlocking means associated with said switches for preventing the motor from being disconnected from the power source while the resistor-shunting switches controlled by the controller are closed.

2. In a motor-control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a plurality of resistor sections connected in series-circuit relation and in series with the motor to control the motor plurality or separately operable shunting the resistor sections, means for automatically accelerating the motor, a. controller for controlling the energization of said switching means'and said resistor-shuntingswitches independently of the automatic accelerating means, and electrical interlocking means associated with said switches and cooperating with the automatic accelerating means for causing the resistor-shunting switches controlled by the controller to be opened in a predetermined sequence betore the motor can be disconnected from the power source.

3. In a motor-control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a plurality of resistor sections connected in series-circuit relation and in series with the motor to control the motor current, a plurality of mechanically independent switches for shunting the resistor sections, means for automatically accelerating the motor, a controller for controlling the energization of said switching means and said resistor-shunting switches independently of the automatic accelerating means, and electrical interlocking means associated with said switching means and said resistor-shunting switches and cooperating with the automatic accelerating means for causing the resistor shunting switches controlled by the controller to be opened in a predetermined .troller for con sequence. before the switching means can be operated to. disconnect powersouroe.

4. Inia motor-control system, incombination power: for the" motor,,

a motor, a: sourcejot switching-t means; for: connecting. the motor to. the power source, acontroller for: controlling.

the: energization of. said switching means, means.

for. operating: the controller, means for auto matically controlling: the acceleration of. the motor; means for operating the acceleration controlling means; and'means' associated with the controller. to: cause the: acoeleration-con-- trolling means to be retained: in any, position by a slight movement of the. controller: operat; ing means the controller: remaining stationary.

5; In a motorecontrol system', iii-combination, a motor, a source of power for the motor, switching means for connecting the motor to the: power source, a manually-operable con trolling the energization of' said switching means, means for: automatically controlling the acceleration of the motor, means for operating the acceleration-controlling means, and means incorporated in the controller to cause the acceleration controlling means to be retained in any position by a slight backward movement of the controller handle only, the controller stationary.

6. In a motor-control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a drum controller for controlling the energization of said switching means, a sequence switch for automatically controlling the acceleration of the motor, means for operating the sequence switch, and means associated with said controller to cause the sequence switch to be retained in any position by a slight backward movement of the controller handle only, the controller drum remaining stationary.

7. In a motor-control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a drum controller for controlling the energization of said switching means, a sequence switch for automatically controlling the acceleration of the motor, means for operating the sequence switch, and a lost motion device associated with the handle of said controller dis posed to cause the sequence switch to be retained in any position by a slight backward movement of the controller handle only, the controller drum remaining stationary.

8. In a motor control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a controller for controlling the energization of said switching means, a plurality of resistor sections to control the current supplied the motor, a plurality of accelerating switches for shunting the resistor sections, means for controlling the operation of the accelerating switches, a relay responsive to the current flowing in the motor for controlling the actuation of the accelerating switch controlling means, said relay having an actuating coil and a plurality of loading coils disposed to oppose the actuating coil, and means associated with the controller for successively energizing the loading coils to vary the current required to actuate the relay, whereby the rate of acceleration of the motor may be varied by advancing the controller.

the: motor: from. the;

drum remaining 9. In a motor-control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a controller for controlling the energization of said switching means, a plurality of resistor sections to control the current supplied to the motor, a plurality of accelerating switches for shunting the resistor sections, means for controlling the operation of the accelerating switches, a relay responsive to the current flowing in the motor for controlling the actuation of the accelerating switch controlling means, said relay having an actuating coil and a plurality of loading coils disposed to oppose the actuating coil, means associated with the controller for successively energizing the loading coils to vary the current required to actuate the relay, a resistor for controlling the current in the loading coils and means on the controller for shunting said resistor, whereby the rate of acceleration of the motor may be varied by advancing the controller.

10. In a motor-control system, in combination, a motor, a source of power for the motor, switching means for connecting the motor to the power source, a plurality of resistor sections connected in series with the motor to control the motor current, a plurality of switches for shunting the resistor sections, a controller for controlling the energization of said switching means and said resistor-shunting switches, a. sequence switch for automatically controlling the acceleration of the motor, electrical interlocking means associated with said switching means and said resistor-shunting switches for normally causing the resistor shunting switches to be opened in a predetermined sequence before the switching means operates to disconnect the motor from the power source, and means disposed on said sequence switch for ensuring the opening of said switching means in the event of failure of the electrical interlocking means to function properly.

NORMAN H. WILLBY. 

